The present invention pertains to an inkjet ink comprising performance additives and to an ink set comprising this ink wherein the performance additives alleviate bleed in multicolor printed elements.
Inkjet printing is a non-impact printing process in which droplets of ink are deposited on a substrate, such as paper, to form the desired image. The droplets are ejected from a printhead in response to electrical signals generated by a microprocessor.
Bleed is a particular problem in ink jet printing because the relatively low viscosity inks used therein tend to spread and because ink jet printers have the capability of printing three or four primary colors in simultaneous (or near simultaneous) fashion.
Various methods have been proposed to prevent bleed of adjacent printing liquids. One method is to apply the two printing liquids at a distance from one another such that no intermingling or mixing of the printing liquids can occur. This method is not a solution to the problem, however, and produces images having poor resolution.
Another method involves delay in applying the second printing liquid until the first printing liquid is completely dry. This method is also disadvantageous, not only because of its inefficiencies, but also because it is not entirely effective.
U.S. Pat. No. 5,091,005 teaches that the addition of formamide to the inks will reduce the occurrence of bleed in some circumstances.
Yet another approach to control bleed is to increase the rate of penetration of the printing liquid into the substrate, but this tends to reduce the optical density.
U.S. Pat. No. 5,116,409 discloses the use of zwitterionic surfactants or nonionic amphiphiles in concentrations above their respective critical micelle concentration. The formation of micelles containing dye molecules is said to prevent the dye molecules in each ink from mixing.
U.S. Pat. No. 5,181,045 teaches a method of ink jet printing wherein one of inks contains a dye that becomes insoluble under defined pH conditions and the other ink has a pH that renders the dye contained in the first ink insoluble.
U.S. Pat. No. 5,488,402 discloses a method for preventing color bleed between two different color ink compositions wherein the first ink is anionic and comprises a coloring agent which includes one or more carboxyl and/or carboxylate groups, and the second ink includes a precipitating agent which is designed to ionically crosslink with the coloring agent in the first ink to form a solid precipitate in order to prevent bleed between the two ink compositions. Multivalent metal salts are disclosed as being useful as the precipitating agent.
U.S. Pat. No. 5,518,534 discloses an ink set for alleviating bleed in multicolor printed elements employing a first ink and a second ink, each containing an aqueous carrier medium and a colorant; the colorant in the first ink being a pigment dispersion and the second ink containing a salt of an organic acid or mineral acid having a solubility of at least 10 parts in 100 parts of water at 25° C., wherein the salt is present in an amount effective to alleviate bleed between the first and second inks.
All of the above-identified publications are incorporated by reference herein for all purposes as if fully set forth.
The known methods of controlling bleed have various advantages and drawbacks, and there is still a need for alternative bleed control methods.